Microphysiological systems, or organs-on-chips, are emerging as a way for scientists to study the effect that drugs, cosmetics and diseases may have on the human body, without needing to test on animals. The problem is, manufacturing and retrieving data from them can be a costly and time-consuming process. Now researchers at Harvard have developed new materials to enable them to 3D print the devices, including the integrated sensors to easily gather data from them over time.

At around the size of a USB stick, organs-on-chips use living human cells to mimic the functions of organs like the lungs, intestines, placenta and heart, as well as emulate and study afflictions like heart disease. But as promising as the technology is, making the chips is a delicate, complicated process, and microscopes and high-speed cameras are needed to collect data from them.

"Our approach was to address these two challenges simultaneously via digital manufacturing," says Travis Busbee, co-author of the paper. "By developing new printable inks for multi-material 3D printing, we were able to automate the fabrication process while increasing the complexity of the devices."

In all, the Harvard team developed six custom 3D-printable materials that could replicate the structure of human heart tissue, with soft strain sensors embedded inside. These are printable in one continuous and automated process and separate wells in the chip host different tissues.

Six custom inks are used to 3D print the devices in a single automated procedure(Credit: Lori K. Sanders and Alex D. Valentine, Lewis Lab/Harvard University)

"We are pushing the boundaries of three-dimensional printing by developing and integrating multiple functional materials within printed devices," says Jennifer Lewis, another of the paper's co-authors. "This study is a powerful demonstration of how our platform can be used to create fully functional, instrumented chips for drug screening and disease modeling."

The incorporated sensors allow the researchers to study the tissue over time, particularly how their contractile stress changes, and how long-term exposure to toxins may affect the organs.

"Researchers are often left working in the dark when it comes to gradual changes that occur during cardiac tissue development and maturation because there has been a lack of easy, non-invasive ways to measure the tissue functional performance," says Johan Ulrik Lind, first author of the study and postdoctoral fellow at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS). "These integrated sensors allow researchers to continuously collect data while tissues mature and improve their contractility. Similarly, they will enable studies of gradual effects of chronic exposure to toxins."

The research was published in the journal, Nature Materials, and a time-lapse of the 3D printing process can be seen in the video below.

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